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Old 06-21-2024, 05:27 AM   #1
Skoolie
 
Join Date: Jul 2023
Location: OKC, OK
Posts: 153
Year: 2010
Chassis: Bluebird Vision
Engine: Cummins 6.7 ISB Allison 2500
Rated Cap: ADA Lift Bus Lift Removed
2002 Freightliner FS65 Cummins 5.9ISB Lift Pump???

I have a 2002 Feightliner FS65 Thomas with Cummins 5.9 ISB. It got stuck in some wet mud one day. Next day went out to get it out and rocked it a bit and it just started to dig the rear wheels into a hole so I stopped and figured I'd have to wait til it dried out. While the engine was idling, it just shut off and wouldn't restart. I let it sit a few days for the grond to dry out. It never started, but would with an unleaded rag prime in the air box then shut off immediately. So I replaced the fuel filters. Both filters were bone dry when I took them off. I filled the new filters with fresh diesel. Cranked a bit, but it started and ran for about a full minute and shut off and will not start again.

I'm guessing the lift pump isn't getting fuel to the filters? The injection pump was obvisouly able to pull fuel out of the filters for it to start and run for a minute.

So does it seem to be a lift pump to everyone else too? Can it possibly be a fuel pump relay? Anyone know if it's an in tank or outside tank pump and where is it located? Where would the fuel pump relay be located?

It ran fantastic up until this day. I was also wondering if the rear end of the bus sitting much lower in the rear now that the rear wheels are in a hole would have anything to do with it? Maybe a weak lift pump? Guage shows 1/2 tank and I have no reason to believe it's wrong, but I did add 5 gallons of diesel to the 1/2 tank just in case, that might be why it wasn't picking up fuel.

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Old 06-21-2024, 07:42 AM   #2
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Pump should be on the side of the block, down and back from the fuel filter.

Bump the key to start, but don't start it, and see if you hear it humming away down there. If you don't, congrats! you found the weak link in that era ISB. Replace it with the upgraded "airtex" style pump that used to be available at every parts store.
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Old 06-21-2024, 09:56 AM   #3
Skoolie
 
Join Date: Jul 2023
Location: OKC, OK
Posts: 153
Year: 2010
Chassis: Bluebird Vision
Engine: Cummins 6.7 ISB Allison 2500
Rated Cap: ADA Lift Bus Lift Removed
Quote:
Originally Posted by Booyah45828 View Post
Pump should be on the side of the block, down and back from the fuel filter.

Bump the key to start, but don't start it, and see if you hear it humming away down there. If you don't, congrats! you found the weak link in that era ISB. Replace it with the upgraded "airtex" style pump that used to be available at every parts store.
Thanks so much. I was thinking it would be back closer to the tank since it's an electric pump, or so I thought. So it's obviously a common issue? No need to consider possibly a fuel pump relay? I was reading something where more than a relay, the pump has a control module that communicates with the ECM. I wasn't sure if that was this model or not.

That's scary, that an airtex is better. I hate airtex brand electric in tank fuel pumps. Seems like they are junk when it comes to GM vehicles. I learned even with lifetime warranty they're not worth it with all the labor involved to change them. I get either AC Delco or Delphi in tank fuel pumps for GM vehicles now. I'll take your word for it that they're better.
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Old 06-21-2024, 04:38 PM   #4
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Very common. No need for a relay, voltage supply isn't an issue. ECM actually monitors amp draw to see if the pump is working and will throw a code and light if it isn't. Some even had a retrofit sensor installed for fuel pressure that would turn on a light as well iirc.

Anywho, stop running it like you were, as that can quickly damage the pump. And I said airtex style, not an airtex pump itself. We actually installed delphi units IIRC. Had no issues and they were much better pumps. Original was a Carter 4070 derivative. It worked okay when new and stock, was marginal with any age or lack of fuel filter maintenance. There was an extension harness so that you could relocate the pump back by the water separator. Idk if they're common much anymore, that stuff is all getting old and not so common.
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Old 06-21-2024, 11:37 PM   #5
Skoolie
 
Join Date: Jul 2023
Location: OKC, OK
Posts: 153
Year: 2010
Chassis: Bluebird Vision
Engine: Cummins 6.7 ISB Allison 2500
Rated Cap: ADA Lift Bus Lift Removed
Quote:
Originally Posted by Booyah45828 View Post
Very common. No need for a relay, voltage supply isn't an issue. ECM actually monitors amp draw to see if the pump is working and will throw a code and light if it isn't. Some even had a retrofit sensor installed for fuel pressure that would turn on a light as well iirc.

Anywho, stop running it like you were, as that can quickly damage the pump. And I said airtex style, not an airtex pump itself. We actually installed delphi units IIRC. Had no issues and they were much better pumps. Original was a Carter 4070 derivative. It worked okay when new and stock, was marginal with any age or lack of fuel filter maintenance. There was an extension harness so that you could relocate the pump back by the water separator. Idk if they're common much anymore, that stuff is all getting old and not so common.
The good news is, I went back out there tonight with a fresh battery to see if the pump was working. I couldn't hear it with all the electric brake motor and buzzers going off. So I had held my hand on the pump and had my dad turn the key to on and I could feel the pump pulse then off. Which I figured meant the filters were full. Opened the water separator valve a bit and seen a ton of air bubbles blurp to the top of the bottom cap and though maybe just air in the filters. Took the lid off the fuel filter and it was down to 1/4 full after I had filled it yesterday, so I filled it again. Cranked on it, and it started and stayed started. Let it run about 15 minutes to charge the batteries and varried the high idle off and on a few times and then finally moved it out of the hole the rear wheels were sitting in and it kept running. Shut it off. Started it again 20 minutes later and it started right up. Sooooo, I think was the filters as I figured, just that I had some air in the filters and lines. Seems fine now that the air is out. Thanks for the tips. Now I know where the pump is and know there's no relay. I figured it was likely ECM controlled when I seen "Module" instead of relay in some fuel system literature.

Ahhh OK, so I get it on the airtex. Yep, Delphi is my preference over the Chyneese aftermarkets. Chyna Chyna Chyna !!!
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Old 06-22-2024, 09:24 AM   #6
Bus Geek
 
Join Date: May 2014
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You shouldn't have air in there ever unless you've drained it or replaced the fuel filters. air leaking in/fuel leaking out overtime shows an issue. Prime suspect is the drain valve on the filter housing, second would be the sealing washers on the banjo fittings, followed by the compression fittings on the nylon hose.

Next time you want to purge the air after a filter change, bump the key to start like I said in my first post, and the ecm will power the pump for 30 seconds or so. I don't like adding unfiltered fuel into filters, but with a cartridge filter, it can be done certain ways and not cause issues.

I wouldn't call it fixed, but you can do what you want.
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Old 06-22-2024, 12:24 PM   #7
Skoolie
 
Join Date: Jul 2023
Location: OKC, OK
Posts: 153
Year: 2010
Chassis: Bluebird Vision
Engine: Cummins 6.7 ISB Allison 2500
Rated Cap: ADA Lift Bus Lift Removed
Quote:
Originally Posted by Booyah45828 View Post
You shouldn't have air in there ever unless you've drained it or replaced the fuel filters. air leaking in/fuel leaking out overtime shows an issue. Prime suspect is the drain valve on the filter housing, second would be the sealing washers on the banjo fittings, followed by the compression fittings on the nylon hose.

Next time you want to purge the air after a filter change, bump the key to start like I said in my first post, and the ecm will power the pump for 30 seconds or so. I don't like adding unfiltered fuel into filters, but with a cartridge filter, it can be done certain ways and not cause issues.

I wouldn't call it fixed, but you can do what you want.
I did replace the filters. The filter, not the water separator was in bad shape. I poured fuel in them before installing. After doing that, it started and ran for about a minute then shut off and wouldn't restart. Assuming that must be when air got in. It's starting and running fine now.
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Old 06-27-2024, 09:19 AM   #8
Bus Nut
 
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I think you ran it till the pickup in the tank sucked air while the back end was in the hole. Remember you said you added 5 gal of fuel to the tank.
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Old 06-27-2024, 06:29 PM   #9
Skoolie
 
Join Date: Jul 2023
Location: OKC, OK
Posts: 153
Year: 2010
Chassis: Bluebird Vision
Engine: Cummins 6.7 ISB Allison 2500
Rated Cap: ADA Lift Bus Lift Removed
Quote:
Originally Posted by Mekanic View Post
I think you ran it till the pickup in the tank sucked air while the back end was in the hole. Remember you said you added 5 gal of fuel to the tank.
I was thinking maybe because I don't know if the fuel gauge is accurate or not. Fuel guage was showing over half tank. So since it was sitting with the rear wheels in the holes when it shut off, I thought maybe the gauge was wrong so to be sure I added the 5 gallons. When that didn't make a difference I replaced the fuel filters that hadn't been changed in years. Of course the bus sat for a few years is why. The fuel filter closest to the injector pump was dry and blowing through it, it don't seem to want to let any air through it so I figured that was it. Replaced the filters and filled them up, it started. Ran about a minute or 2 and shut back off. I do think I had air in it for sure during the filter replacment. I opened the valve on the water separator and it blurp blurp blurped air bubbles a few times. I re filled the one closest to the injector pump, it started and has been running every since.
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Old 06-27-2024, 07:18 PM   #10
Bus Nut
 
Join Date: Jan 2015
Posts: 258
If it has one of the larger 100 gal tanks adding 5 gal is hard to see gauge movement.
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